Can't attach image with https://xxxx.ui.nabu.casa/api/hassio_ingress/yyyy/picture/1/current/

I can not attached an image located at https://xxxx.ui.nabu.casa/api/hassio_ingress/yyyy/picture/1/current/ to a notification.
Address is from motioneye Snapshot URL.
When checking this address through the Web Explorer, I can see the most recent picture generated by motioneye.
Is this a whitelist issue? Do I need to state a file name (jpg)?
I am not using a service call here.